Active Pull-Down for Compensated Current Switch Emitter Follower
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
The fall-time delay of an internally compensated current switch emitter follower is raised significantly when its output emitter follower must drive a heavy load, for example, a large fan-out or a long on-chip line. By adding the active pull-down device described in this article, the drive capability of the CCSEF is improved and the fall-time delay significantly reduced. Fig. 1 shows the circuit of a compensated current switch emitter follower (CCSEF). When the emitter follower must drive a heavy load, the transistor T OUT will "turn off", thereby reducing its drive capability and significantly increasing the fall-time and delay of the output voltage, as shown in Fig. 2. The addition of an active pull- down device, conceptually shown in Fig.